qapi: Avoid use of misnamed DO_UPCAST()

The macro DO_UPCAST() is incorrectly named: it converts from a
parent class to a derived class (which is a downcast).  Better,
and more consistent with some of the other qapi visitors, is
to use the container_of() macro through a to_FOO() helper.  Names
like 'to_ov()' may be a bit short, but for a static helper it
doesn't hurt too much, and matches existing practice in files
like qmp-input-visitor.c.

Our current definition of container_of() is weaker than
DO_UPCAST(), in that it does not require the derived class to
have Visitor as its first member, but this does not hurt our
usage patterns in qapi visitors.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <1454075341-13658-3-git-send-email-eblake@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

1 files changed, 13 insertions, 8 deletions

diff --git a/qapi/string-output-visitor.c b/qapi/string-output-visitor.c
index b04cec4cf7..b0313cb53a 100644
--- a/qapi/string-output-visitor.c
+++ b/qapi/string-output-visitor.c
@@ -67,6 +67,11 @@ struct StringOutputVisitor
     GList *ranges;
 };
 
+static StringOutputVisitor *to_sov(Visitor *v)
+{
+    return container_of(v, StringOutputVisitor, visitor);
+}
+
 static void string_output_set(StringOutputVisitor *sov, char *string)
 {
     if (sov->string) {
@@ -120,7 +125,7 @@ static void format_string(StringOutputVisitor *sov, Range *r, bool next,
 static void print_type_int(Visitor *v, int64_t *obj, const char *name,
                            Error **errp)
 {
-    StringOutputVisitor *sov = DO_UPCAST(StringOutputVisitor, visitor, v);
+    StringOutputVisitor *sov = to_sov(v);
     GList *l;
 
     switch (sov->list_mode) {
@@ -196,7 +201,7 @@ static void print_type_int(Visitor *v, int64_t *obj, const char *name,
 static void print_type_size(Visitor *v, uint64_t *obj, const char *name,
                            Error **errp)
 {
-    StringOutputVisitor *sov = DO_UPCAST(StringOutputVisitor, visitor, v);
+    StringOutputVisitor *sov = to_sov(v);
     static const char suffixes[] = { 'B', 'K', 'M', 'G', 'T', 'P', 'E' };
     uint64_t div, val;
     char *out;
@@ -227,14 +232,14 @@ static void print_type_size(Visitor *v, uint64_t *obj, const char *name,
 static void print_type_bool(Visitor *v, bool *obj, const char *name,
                             Error **errp)
 {
-    StringOutputVisitor *sov = DO_UPCAST(StringOutputVisitor, visitor, v);
+    StringOutputVisitor *sov = to_sov(v);
     string_output_set(sov, g_strdup(*obj ? "true" : "false"));
 }
 
 static void print_type_str(Visitor *v, char **obj, const char *name,
                            Error **errp)
 {
-    StringOutputVisitor *sov = DO_UPCAST(StringOutputVisitor, visitor, v);
+    StringOutputVisitor *sov = to_sov(v);
     char *out;
 
     if (sov->human) {
@@ -248,14 +253,14 @@ static void print_type_str(Visitor *v, char **obj, const char *name,
 static void print_type_number(Visitor *v, double *obj, const char *name,
                               Error **errp)
 {
-    StringOutputVisitor *sov = DO_UPCAST(StringOutputVisitor, visitor, v);
+    StringOutputVisitor *sov = to_sov(v);
     string_output_set(sov, g_strdup_printf("%f", *obj));
 }
 
 static void
 start_list(Visitor *v, const char *name, Error **errp)
 {
-    StringOutputVisitor *sov = DO_UPCAST(StringOutputVisitor, visitor, v);
+    StringOutputVisitor *sov = to_sov(v);
 
     /* we can't traverse a list in a list */
     assert(sov->list_mode == LM_NONE);
@@ -266,7 +271,7 @@ start_list(Visitor *v, const char *name, Error **errp)
 static GenericList *
 next_list(Visitor *v, GenericList **list, Error **errp)
 {
-    StringOutputVisitor *sov = DO_UPCAST(StringOutputVisitor, visitor, v);
+    StringOutputVisitor *sov = to_sov(v);
     GenericList *ret = NULL;
     if (*list) {
         if (sov->head) {
@@ -293,7 +298,7 @@ next_list(Visitor *v, GenericList **list, Error **errp)
 static void
 end_list(Visitor *v, Error **errp)
 {
-    StringOutputVisitor *sov = DO_UPCAST(StringOutputVisitor, visitor, v);
+    StringOutputVisitor *sov = to_sov(v);
 
     assert(sov->list_mode == LM_STARTED ||
            sov->list_mode == LM_END ||